1. Field of the Invention
The present invention relates to a piezoelectric device for use as a drive source for an injector.
2. Description of the Related Art
Injectors (fuel injection devices) for an automobile internal combustion engine are constructed to inject fuel, for example, by putting nozzle needles in open condition by altering the pressure imparted to the nozzle needles through switching the open/close conditions of fuel passages by moving valve elements of three-way or two-way valves connected to a common rail in which high-pressure fuel is accumulated.
Then, in general, electromagnetic valves are used as drive sources for moving the valve elements. On the other hand, there have been attempts to use piezoelectric devices as the drive sources in order to precisely control the fuel injecting conditions by controlling in turn the drive sources finely.
However, there has not yet been put into practice any injector employing a piezoelectric device.
This is because the piezoelectric devices for injectors need to be compact in size and be able to be mass produced easily and consistently while ensuring quality.
Japanese Unexamined Utility Model Publication (U.M. Kokai) No. 55-71571 discloses a conventional piezoelectric device. As shown in FIG. 18, in this conventional piezoelectric device, an insulating protection layer 95 made from elastic epoxy resin is disposed around the outer circumference of a piezoelectric device 9, and thereafter metallic blocks 96, which are larger in diameter than the piezoelectric device, are disposed at both ends of the piezoelectric device in the stretching direction thereof.
With this conventional piezoelectric device 9, the provision of the metallic blocks 96 produces waste space in an installation space in the injector where the piezoelectric device is installed, and therefore the conventional piezoelectric device cannot meet the demand for miniaturization of the injector.
In addition, since the metallic blocks 96 need to be disposed on the piezoelectric device after the insulating protection layer 95 has been provided thereon, assembling the piezoelectric device to the injector becomes complex. Additionally, as shown in FIG. 19, there is a drawback in that unnecessary protruding portions 959 are formed on an end of the piezoelectric device when the insulating protection layer 95 is formed.
Furthermore, an adhesive has to be used to fix abutment members such as the metallic blocks integrally on upper and lower surfaces of the piezoelectric device. In this case, however, the stretching movement of the piezoelectric device is transmitted via the adhesive, and therefore, this may lead to a risk that generated force is lost.
The invention was developed in light of the above conventional drawbacks, and an object thereof is to provide a piezoelectric device which is compact in size and easy to produce and which exhibits superior generated force.
According to the invention, there is provided a stacked piezoelectric device comprising a plurality of piezoelectric layers and electrode layers which are stacked in alternate fashion, the stacked piezoelectric device being characterized by provision of an abutment member which is brought into direct abutment with at least one end face of the piezoelectric device in a stretching direction thereof and a coating member having electric insulating properties which covers at least part of the abutment portion between the abutment member and the piezoelectric device so that the state is maintained in which the abutment member and the piezoelectric device are in abutment with each other.
According to the invention, as described above, the abutment member is brought into abutment with the end face of the piezoelectric device in the stretching direction thereof, and the abutment state is maintained with the coating member.
Since no adhesive is interposed between the abutment member and the piezoelectric device, this allows the stretching movement of the piezoelectric device to be directly transmitted to the abutment member, whereby superior generated force can be maintained.
In addition, since the joined condition of the abutment member to the piezoelectric member is maintained by the coating member, the abutment member and the piezoelectric device can be handled as one piece with ease, thereby facilitating case of production.
Moreover, the provision of the abutment member ensures that the coating member is prevented from protruding from the end face of the piezoelectric device in the stretching direction thereof when the coating member is disposed, further facilitating production of the piezoelectric device.
Thus, according to the invention, there is provided a piezoelectric device which is compact in size and easy to produce and which exhibits superior generated force.
Next, according to the invention, there is provided a method for producing a stacked piezoelectric device comprising a plurality of piezoelectric layers and electrode layers which are stacked in alternate fashion, the method comprising the steps of bringing an abutment member into direct abutment with at least one end face of the piezoelectric device in a stretching direction thereof and clamping the piezoelectric device with a pair of fixtures from both ends of the piezoelectric device in the stretching direction thereof, next supplying a coating material having fluidity to at least an outer circumference of the abutment portion of the abutment member to the piezoelectric device, and allowing the coating material to set to thereby form a coating member for maintaining the abutment condition of the abutment member to the piezoelectric device.
According to the method of the invention, unitization of the abutment member and the piezoelectric device is ensured with the coating member without using an adhesive, thereby making it possible to obtain a superior piezoelectric device.
Various methods can be used as the method for supplying the coating material, and include dripping by a dispenser, coating by a roller coater, spraying, dipping and the like.
The invention may be more fully understood from the description of preferred embodiments thereof, as set forth below, together with the accompanying drawings.